﻿using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Lazy
{
    class Program
    {
        static void Main(string[] args)
        {
            const double a = 3.14;
            Console.WriteLine("请输入圆的半径：");
            string r = Console.ReadLine();

           double R = Convert.ToDouble(r);

            Console.WriteLine("该圆的面积是：" + a * R * R);
            Console.ReadKey();
        }
    }
}
